The objectives outlined in this proposal from the Medical Physics Section, University of Wisconsin, are to design, construct and evaluate ultrasonic tissue-equivalent phantoms for the breast. The purpose of this work is to create standardized objects with realistic acoustic structures and targets for assessing imaging capabilities of state-of-the-art ultrasonic breast scanning equipment. Phantoms will be constructed using tissue equivalent gelatins for mimicking various breast constituent tissues. An iterative approach to phantom development is facilitated by this material since it is readily available, can be produced with acoustic parameters matching those of different soft tissues, and is easily worked with. Starting deigns for phantoms will be based upon anatomical sections of breast tissue, available in our laboratory as well as in the literature. Further developmental work of the phantom material is proposed, primarily in order to match small particle scattering with scattering observed in breast tissues. A major portion of the effort will be devoted to the development of construction techniques or the incorporation of structures of suffiicient geometric complexity to provide acoustic interfaces and mimicked tissue volumes which are representative of those encountered in vivo. Evaluation of phantoms will be carried out in part in laboratories where advanced ultrasonic breast imaging systems are being designed and employed.